Is it allergy season in Washington?

No other state has a more dramatic east-west allergy divide than Washington. The Cascade Mountains act as a climatic wall — trapping Pacific moisture on the western side and creating a dry continental climate to the east. Seattle and Spokane, just 280 miles apart, experience fundamentally different allergen profiles. Western Washington's maritime climate keeps mold elevated year-round but suppresses grass pollen. Eastern Washington's dry, agricultural Palouse produces some of the highest grass counts in the country in June–July.

Washington's geography is the key to understanding its allergy calendar. The Cascade Range isn't just a mountain range — it's a climate boundary that creates entirely different plant communities on either side. Knowing which side of the mountains you're on tells you most of what you need to know about your allergy season.

Puget Sound / Seattle Metro

Alder in February — then marine layer helps moderate the season

Alder is the signature Western WA allergen. It starts in February — sometimes January in mild winters — and peaks in March. Seattle's famous overcast drizzle actually helps: wet days wash pollen out of the air. But sunny spring stretches (and there are more than people expect) see very high alder and birch counts. Grass season is milder than eastern WA.

Alder · Feb–AprBirch · Mar–MayOak · Apr–JunGrass (mild) · May–Jul

Tacoma / South Puget Sound

Similar to Seattle with slightly less marine moderation

Tacoma follows Seattle's general pattern but sits slightly further from Puget Sound's moderating influence. Alder and birch February–April, grass more prominent through summer. The agricultural land in Pierce County adds a grass dimension not as prominent in Seattle proper.

Alder · Feb–AprBirch · Mar–MayGrass · May–JulRagweed · Aug–Sep

Cascade Foothills

Transitional zone — both western and eastern species present

The transitional zone between Puget Sound and the dry east includes cities like Yakima (west slopes), Cle Elum, and Leavenworth. Higher elevation delays tree pollen 2–3 weeks. Both alder (western) and juniper/cedar (eastern) occur here. Snowpack keeps spring compressed.

Alder + Juniper overlapOak · May–JunGrass · Jun–AugRagweed · Aug–Sep

Eastern Washington / Spokane / Palouse

Dry agricultural belt — intense grass June–July, sagebrush in fall

Eastern Washington is a completely different world from Seattle. The Palouse wheat fields and dry rangeland produce very high grass pollen counts — Timothy and brome run May through July. Sagebrush and mugwort take over August–September as the dominant weed allergens. Alder isn't significant east of the Cascades; juniper cedar becomes the winter tree allergen instead.

Grass · May–Jul (Very High)Sagebrush · Aug–SepRagweed · Aug–SepJuniper · Jan–Feb

Each row shows trees (blue), grasses (green), and weeds (amber) for one region. Note how dramatically Eastern WA's grass row differs from Seattle's.

Oral Allergy Syndrome (also called pollen-food allergy syndrome) causes tingling or mild itching in the mouth when you eat certain raw foods during the relevant pollen season. The proteins in the food are similar enough to the pollen protein that your immune system cross-reacts. Cooking usually deactivates the offending protein, so the same food cooked may cause no reaction.

Alder & Birch pollen

Stone fruits & apples

Apples, peaches, cherries, plums, pears, almonds, hazelnuts, carrots, celery

Peak risk February–April in Western WA. Alder cross-reacts with the same Bet v 1 proteins as birch — making Western Washington one of the highest-risk regions in the US for stone fruit OAS. The Pacific Northwest's apple and cherry orchards are the same foods that trigger reactions.

Grass pollen

Tomatoes, potatoes & melons

Tomatoes, potatoes, kiwi, watermelon, cantaloupe, oranges (in some cases)

Peak risk May–July in Western WA; dramatically more intense in Eastern Washington during the Palouse grass season. Eastern WA residents may notice food reactions that are absent when visiting Seattle.

Ragweed / Mugwort / Sagebrush

Melons & bananas

Watermelon, cantaloupe, honeydew, banana, zucchini, cucumber, sunflower seeds

Peak risk August–September. Sagebrush and mugwort are the dominant weed allergens in Eastern Washington and cross-react more broadly than ragweed alone. Western WA ragweed is milder.

Not medical advice. If you suspect OAS, speak with an allergist — it can sometimes progress, and symptoms that extend beyond the mouth should be evaluated.